1. Field of the Invention
The present invention relates to a control method and a control system for delivering information to mobile terminal through mobile communication network. The present invention further relates to an information storage method which is performed at each node in the mobile communication network where information is delivered in accordance with the control method.
2. Description of the Related Art
A control method for delivering information using the cache function of the fixed communication network is defined in the standards, RFC2186 (Internet Cache Protocol, Version 2) and RFC2187 (Application of Internet Cache Protocol, Version 2). In the mobile communication network where the control method for delivering information complying with the standards, the existence of a cache node along the route through which data is transferred is checked before a mobile terminal downloads the data. If a cache node exists in the delivery channel, the information delivery is performed through the cache node.
A communication system in which the information delivery is performed in compliance with the control method for delivering information to fixed terminals are configured as shown in FIG. 1, for example. The Internet Cache Protocol is utilized as the control method for delivering information.
In FIG. 1, the communication network includes communication nodes N1–N6 each functioning as a router and communication nodes 21, 22, 31, and 41 each functioning as a router and a cache (hereinafter referred to as “cache nodes”). The local cache node 21 (LC-1) is connected to the parent cache node 31 (PC-1) through the communication node N3 and the subsidiary cache node 22 (SC-1) through the communication node N2. The parent cache node 31 is connected to the grand parent cache node 41 (GC-1) through the communication nodes N4 and N5. The grand parent cache node 41 is connected to the internet INT where a host server 50 (SVR) exists, through the communication node N6.
Client terminals 101(C1), 102(C2), 103(C3) are connected to the local cache node 21 through the communication node N1. They receive information delivery service from the communication network where the local cache node 21, the parent cache node 31, and the grand parent cache node 41 each having a cache function are arranged in a hierarchy.
In the network system described above, information “D” stored in the host server SVR is transferred to the client terminal 101(C1), for example, in the following manner.
A request for delivery of the information D sent by the client terminal 101 is transferred to the local cache node 21 through the communication node N1. The local cache node 21 checks whether it stores the information D, and if it does not store the information D, it transfers the request for delivery toward the communication node N3. In response to the reception of the request for the delivery, the parent cache node 31 checks whether it stores the information D, and if it does not store the information D, it further transfers the request for delivery toward the communication node N4. The request for delivery is transferred to the grand parent node 41 through the communication nodes N4 and N5. As described above, if no cache node stores the information D which is requested by the client 10, the request for delivery is transferred to the communication nodes (including cache nodes) sequentially.
The request for delivery of the information D is finally transferred to the host server 50 in the internet INT. The host server 50 delivers the information D toward the client terminal 101 through the internet INT. The information D delivered by the host server 50 is delivered to the client terminal 101 through each communication nodes (including cache nodes).
As shown in FIG. 2, in the process in which the information D is delivered from the host server 50 to the client terminal 101, the cache nodes, the local cache node 21 and the parent cache node 31 for example, near the client terminal 101 stores (or caches) cache information D′ identical to the information D.
If one of the client terminals 101, 102, 103 issues another request for delivery of the information D, the cache information D′ corresponding to the information D stored in the local cache node 21 is delivered to the client terminal requested for the delivery. Accordingly, the traffic within the communication network is reduced.
Mobile terminals, however, move while receiving the delivery of information, that is, downloading data. Therefore, it is necessary to switch delivery channel while receiving information. Since the switching of the communication channel degrades the efficiency of information delivery, it is not practical to apply the abovementioned method for delivering information complying with the Internet Cache Protocol designed for the fixed communication network to the mobile communication network. For example, while receiving the delivery of cache information from a cache node in the mobile communication network, a mobile terminal, as it moves, switches its connection to cache nodes. That is, the delivery channel between the mobile terminal and the host server is switched. If a new delivery channel does not include a cache node which stores cache information, the cache function of the cache nodes do not work effectively.